The significance of the difference between slow inspiratory and forced expiratory vital capacity

In 112 healthy subjects and 1, 767 patients examined for subjective complaints or assessment of pneumoconiosis, the routine examination of clinical status, chest X-ray and lung function was completed by measurement of forced expiratory vital capacity (FVC) and calculation of the difference between inspiratory and forced expiratory vital capacity (dVC). The results show that only in healthy subjects the difference between slow inspiratory vital capacity (VC) and FVC may be neglected, but in patients both values might differ by more than 1000 ml and cannot replace each other. Airway resistance as measured by body plethysmography cannot be reliably calculated from various spirometric values.